Life Expectancy Evaluation of the Wood Poles Which Support the Hellenic Electrical Distribution Network

The Hellenic electrical distribution lines have been basically supported with the use of wood poles. Outages due to aging, degradation, or broken wood poles may infer significant costs due to repair and loss of energy to consumers. Lifetime estimation of wood poles is significant for maintenance and replacement decisions at the power utility. The paper presents a methodology, based on a statistical analysis, for the evaluation of the life expectancy and the production of a survival curve of a typical Hellenic distribution wood pole in-service. The proposed methodology intends to minimize the life-cycle cost of inspection and refurbishment of wood poles in the distribution network of Hellas, something that is really important in the new competitive and liberating Hellenic electrical energy market.     

Relating indices of knowledge structure coherence and accuracy to skill-based performance: Is there utility in using a combination of indices?

The authors examined the relative criterion-related validity of knowledge structure coherence and two accuracy-based indices (closeness and correlation) as well as the utility of using a combination of knowledge structure indices in the prediction of skill acquisition and transfer. Findings from an aggregation of 5 independent samples (N = 958) whose participants underwent training on a complex computer simulation indicated that coherence and the accuracy-based indices yielded comparable zero-order predictive validities. Support for the incremental validity of using a combination of indices was mixed; the most, albeit small, gain came in pairing coherence and closeness when predicting transfer. After controlling for baseline skill, general mental ability, and declarative knowledge, only coherence explained a statistically significant amount of unique variance in transfer. Overall, the results suggested that the different indices largely overlap in their representation of knowledge organization, but that coherence better reflects adaptable aspects of knowledge organization important to skill transfer. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scouring at Bed Sills as a Response to Flash Floods

The temporal development of clear-water local scour depth at bed sills in uniform gravel beds is considered. Experiments are presented on the development of scour holes under unsteady hydraulic conditions, with the triangular-shaped hydrographs tested being of different durations and different rates of flow variation. Based on the experimental results and a theoretical framework, a method is given for the definition and prediction of the scouring process under unsteady flows in terms of a dimensionless temporal parameter. A “flash flood” is here defined as an event for which the scour doesn’t attain its potential magnitude, i.e., the equilibrium value for the peak hydrograph flow rate. This flood nature is dependent on both the characteristics of the flood event itself and the characteristics of the stream. A quantitative measure of what constitutes a flash flood is given in terms of the identified temporal parameter. Results show that the ratio between the final scour depth and the potential scour depth at a bed sill for a given hydrograph can be estimated as a function of the identified temporal parameter.     

Reduction in thermal conductivity of Bi thin films with high-density ordered nanoscopic pores

We prepared two-dimensional Bi thin films with high-density ordered nanoscopic pores by e-beam evaporation of Bi metal. For this structure, we used polystyrene beads ranging from 200 to 750 nm in diameter as an etch mask. The typical hole and neck sizes of the Bi thin films with approximately 50 nm in thickness on SiO₂/Si substrates were in the range of 135 to 490 nm and 65 to 260 nm, respectively. By measuring the thermal characteristics through a 3ω technique, we found that the thermal conductivities of nanoporous Bi thin films are greatly suppressed compared with those of corresponding bulk materials. With a decrease in pore size to approximately 135 nm, the thermal conductivity decreased significantly to approximately 0.46 W/m·K at 300 K.     

Conceptual Design of Unpressurized Shelters on Lunar Surface

Three concepts for the shelters on the moon are presented here. It is envisaged that the first robots will land on the moon and start preparing sites for advanced bases and also for future human presence. These robots will encounter severe radiation and micrometeor hits when they are exposed to the lunar atmosphere. During the period of intense solar radiation these robots have to be temporarily sheltered, since shielding on the robots may not be adequate to protect the instruments. The construction of these shelters has to be performed with very little equipment support. This paper presents concepts and their feasibility analysis for the fabrication of shelters under such stringent constraints.     

核壳结构PMMA纳米微球增韧R-PVC/CPE

研究了核壳结构聚甲基丙烯酸甲酯（PMMA）纳米微球对硬质聚氯乙烯/氯化聚乙烯（R-PVC/CPE）体系的增韧和增强作用及其对加工流变性的影响。研究发现，核壳结构PMMA纳米微球与R-PVC/CPE基体在适当配比下共混，在显著提高基体的冲击强度的同时，拉伸强度、伸长率和加工流变性也有改善。     

k型往复式给煤机出料量控制技术改进

通过对K型往复式给煤机曲柄壳、调节杆定位调控出料量存在问题的分析,提出了具体可行的改进措施,有效解决了设备的设计缺陷,并将改进的技术成功应用于设备的改造,取得了良好的生产效果。     

Hydroelastic analysis of VLFS based on a consistent coupled-mode system and FEM

Three models for the interaction of water waves with large floating elastic structures are analysed. The first model, based on the Euler–Bernoulli beam theory, has already been extensively studied. The second is based on the Rayleigh beam equation. The third approach utilises the Timoshenko approximation and is thus capable of incorporating shear deformation and rotary inertia effects. A novelty of the proposed hydroelastic systems is the consistent local mode expansion of the underlying hydrodynamic field interacting with the floating structure, which leads to coupled-mode systems with respect to the modal amplitudes of the wave potential and the surface elevation. This representation is rapidly convergent to the solution of the full hydroelastic problem. The dispersion relations of these models are derived and analysed, supporting at a next stage the efficient development of finite element method solvers of the coupled system.